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Exoplanet Loops Over Star's Pole.

Reporting December 18th in Nature, Vincent Bourrier (Geneva University Observatory, Switzerland) and colleagues have found that the Neptune-mass exoplanet GJ 436b orbits around its star's poles rather than its equator. The default in planet formation is for worlds to coalesce from a dusty disk of gas around a newborn star's middle, a consequence of the conservation of angular momentum. Furthermore, huge planets close to their parent stars "should" be on circular, equator-aligned orbits due to tidal interactions. But GJ 436b is wonky: The team's 3D mapping of the planet's trajectory, coupled with measurements of the star's rotation, reveal that the gaseous world is following an elongated orbit that passes over the star's pole. This setup suggests that an outer, unseen exoplanet might have driven GJ 436b inward to its current location. The migration would also have exposed the planet's atmosphere to more starlight and might have triggered GJ 436b's comet-like atmosphere.

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Author:Carlisle, Camille M.
Publication:Sky & Telescope
Article Type:Brief article
Date:Mar 18, 2018
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